bolt problem

Hello All,
I am new to the forum and to AR's.
I purchased my AR-15 about 12 days ago. The first time at the range, unknown by me, I shot about 60 rounds threw the gun before finding out I should clean and lube gun before use. I was told it needed to be cleaned/lubed well by a AZ Ranger...

I have a Ruger MK III Long Rifle pistol. I field-stripped it for the first time yesterday for cleaning. I was careful to follow the instructions in the manual. When I reassembled it, the bolt had trouble sliding back in. When I finished the reassembly, all LOOKED good, but the bold would only go...